Hematology testing is generally performed utilizing two distinct methodologies; cell blood count which enumerates the white cell, red cell and platelet counts; and differential blood count which enumerates the percentages of the types of white cells. Cell blood count is currently being performed in large institutions by automatic electronic instruments such as the popular "Coulter Electronic Blood Cell Counter." Although electronic instruments are under development for determination of the differential blood count by means of image recognition, the technology is complex and the instruments will be necessarily expensive. At the present time, no instrument is commercially available which provides both cell blood count and differential blood count.
For these reasons, differential blood count is still obtained by the traditional method of microscopy. A smear or spun slide is prepared of the patient's blood and at least 200 white cells are manually counted by means of microscopic magnification and classified as to type to determine the percentages of the white cell types in the blood. Since the volume of blood in the microscope field is not known, microscopy to date has not been able to provide absolute cell counts. If it is desired to know the absolute numbers of white cell types in the blood, the percentages derived from the differential blood count must be multiplied by the absolute white cell count derived from the cell blood count.
The electronic instruments utilized in hematology are too expensive for small institutions. Individual physicians and small clinics must rely on specialized laboratories for hematological analysis, and the delay in transporting blood samples to and from the laboratories is sometimes fatal in emergency cases. Another disadvantage of the electronic instruments is that they often malfunction, and must be carefully checked and calibrated on a daily basis.
The admixture of latex beads with blood constituents in itself is not new. A specific application is disclosed in U.S. Pat. No. 3,558,522 in which washed red blood cells and latex beads are mixed together in a fluid suspension to provide a calibration standard for electronic cell blood count instruments. The latex beads replace the white blood cells which are removed by the washing process.
Latex beads are used in the present invention in a completely different and novel manner to enable absolute blood counts to be performed by microscopy, thereby enabling cell blood count and differential blood count analysis to be performed by any person skilled in the art from a single blood sample in a short period of time.